Paul Livingston

Phenomenal Concepts andthe Problem of Acquaintance

Abstract: Some contemporary discussion about the explanation of

consciousness substantially recapitulates a decisive debate about ref-

erence, knowledge, and justification from an earlier stage of the ana-

lytic tradition. In particular, I argue that proponents of a recently

popular strategy for accounting for an explanatory gap between phys-

ical and phenomenal facts — the so-called ‘phenomenal concept

strategy’ — face a problem that was originally fiercely debated by

Schlick, Carnap, and Neurath. The question that is common to both

the older and the contemporary discussion is that of how the presence

or presentation of phenomenal experiences can play a role in justify-

ing beliefs or judgments about them. This problem is, moreover, the

same as what was classically discussed as the problem of acquain-

tance. Interestingly, both physicalist and non-physicalist proponents

of the phenomenal concept strategy today face this problem. I con-

sider briefly some recent attempts to solve it and conclude that,

although it is prima facie very plausible that acquaintance exists, we

have, as yet, no good account of it.

My aim in this paper is to demonstrate that proponents of a recently

popular physicalist strategy for explaining consciousness — what has

been called the phenomenal concept strategy — share with certain

anti-physicalist phenomenal realists a common problem, which was

also a problem for Schlick, Carnap, and Neurath in the days of the

Vienna Circle. Though it has implications for ontology and metaphys-

ics, this problem is essentially one about justification: how can judg-

ments, claims, or beliefs about phenomenal experience be justified, at

Journal of Consciousness Studies, 20, No. 5–6, 2013, pp. ??–??

Correspondence:Email: pmliving@unm.edu

least in part, by the presence or presentation of the relevant experi-

ences themselves? In this paper, I argue on conceptual grounds that all

proponents of the phenomenal concept strategy face this problem, and

on historical grounds that it is indeed a general one, one that may cut

deeper than the contemporary debate between physicalism and phen-

omenalism itself.

I

For the purposes of this paper, I take physicalism (in its contemporary

form) to be an explanatory thesis: if physicalism is right, then all facts

about consciousness are, or at least can be wholly explained in terms

of, physical facts. Nevertheless, it is prima facie plausible that (for

now at least) there is at least an explanatory gap between facts about

consciousness and physical facts: that is, a complete description of the

physical facts does not entail the facts about consciousness.1 What has

come to be called the ‘phenomenal concept strategy’ is not itself a the-

ory of consciousness, but rather a strategy employed mostly by

physicalists to account for why there should at least seem to be an

explanatory gap, even if physicalism is true.2 The underlying idea is

that it is the special features of concepts of consciousnesss that make

for at least the appearance of an explanatory gap between conscious-

ness and the physical world. On this kind of story, the phenomenal

concepts we use to think about our own experiences have distinctive

features that mark them off from the physical concepts we normally

use to think about brain states as such, even though both types of con-

cepts cover what are, in fact, the same things.3 It is this difference in

conceptual features, rather than any difference in the objects concep-

tualized, that explains why there is at least the appearance of an exp-

lanatory gap between experience and the physical world. Conceiving

of our experience using phenomenal concepts (as we usually do)

rather than physical ones, we are apt to miss the fact that physical con-

cepts (e.g. concepts of physiologically or functionally described brain

states) also pick out the very same individuals. Thus, we are apt to

imagine that there is an ontological or metaphysical gap between phe-

nomenal states and the physical world, although in fact (on this tell-

ing) there is no such gap.

2 P. LIVINGSTON

[1] See, e.g. Jackson (1982), Chalmers (1996).

[2] In this paragraph and the next one I largely follow the summary given by Chalmers (2007,pp. 171–2).

[3] In saying that a concept ‘covers’ a particular, I mean that that particular is a particular ofwhichever type the concept picks out.

For many adherents to the phenomenal concept strategy, the most

important distinctive feature of phenomenal concepts is their analogy

to, or actual employment of, indexical linguistic terms or the concepts

corresponding to them. Several philosophers have suggested that phe-

nomenal concepts are themselves indexical concepts or have index-

ical characters in the sense of Kaplan (1989).4 That is, they pick out

their referents (which are in fact neural states, processes, or proper-

ties) in the same way as (or a way closely analogous to the way in

which) linguistic indexical terms like I, now, and this pick out their

referents in discourse. On these theories, the apparent epistemic gap

between phenomenal properties and physical properties is to be under-

stood as analogous to the familiar epistemic gaps that can arise between

claims made about individuals by using indexicals and claims about the

very same individuals made without using indexicals.5

Others have argued on related grounds that phenomenal concepts

are recognitional concepts in the sense that they can be used to pick

out experiences as ‘one of those’, or ‘one of that type’, and so can sub-

sequently be used to recognize individuals as of the same type (e.g.

Loar, 1997; Levin, 2007). Here, the phenomenal concept is treated as

a ‘type-demonstrative’. The idea is that it picks out a general type by

demonstrating or demonstratively referring to a particular of that type.

Doing so might be enough to give us the ability to recognize subse-

quent instances of that type which we encounter, even if we have no

detailed theoretical knowledge of the distinctive features of that type.

If this is right, then successful recognitional use of a phenomenal con-

cept to pick out a type is, again, entirely consistent with failing to real-

ize that there is a physical concept that picks out the same type. Some

proponents of this version of the strategy have additionally suggested

that, in forming or applying concepts of this kind, it is the referent

itself (the phenomenal state being referred to) that serves as a ‘mode of

presentation’ for that very referent (e.g. Loar, 1999).

A third variant of the phenomenal concept strategy holds that phe-

nomenal concepts are unique in that they include, in their constitutive

structure, the very phenomenal states or properties to which they

refer. For instance, phenomenal concepts might have what Papineau

(2002) has described as a quotational structure, something like the

structure of the sentence ‘That state: —’, where the blank is to be

filled with the state itself in a manner analogous to the way a word is

embedded between quotation marks. If this is right, then it might

PHENOMENAL CONCEPTS & ACQUAINTANCE 3

[4] Perry (2001), O’Dea (2002), Ismael (1999).

[5] For this sort of gap, see, e.g. Perry (1979).

again be possible to be in a phenomenal state, and even to conceive of

it under a phenomenal concept of this form, without being able to con-

ceive of it under the purely physical concepts that pick out the neural

state that it in fact is, on the physicalist view.

A fourth version of the phenomenal concept strategy has also been

employed by some anti-physicalists, most prominently Chalmers

(2003; 2007). According to Chalmers, phenomenal states can play a

role in justifying phenomenal beliefs employing phenomenal con-

cepts in part by figuring in those very concepts as constituents. It is

this capability of concepts to include the very individuals they con-

cern as constituents that, according to Chalmers, accounts for the spe-

cial relation of phenomenal experience to the concepts that we use to

think about it.

For all four of these versions of the phenomenal concept strategy, it

is decisively important that we can bear a certain kind of relation to

our own phenomenal states, simply in virtue of having or enjoying

them.6 That is, we stand in a special relationship to our own phenome-

nal states in that they are ours at all, in that they are ‘experientially

present’ or ‘present to mind’, and this relationship plays an essential

role in our forming at least some justified beliefs about them, for

instance about their phenomenal character. It is this relationship that

makes it possible for these states to be presented under phenomenal

concepts at all, and thus for a gap to appear to open up between this

presentation and their presentation under physical concepts. On the

indexical versions of the strategy, for instance, it is my ability index-

ically to pick out a particular, occurring state of a particular (phenom-

enal) type that yields the justified belief that I am enjoying a state of

that type right now. On the recognitional concept versions, similarly, it

is my type-indexical reference to a state I am currently enjoying that

allows me to know that I am enjoying a state of that type (even if I can-

not further specify the type). On the quotational version, it is the

actual occurrence of the state within a larger conceptual structure that

allows me to conceive of it as being of the type that it is; and so on.7

But what is the nature of this relationship, which allows particular

states to present themselves in such a way as to contribute essentially

to producing knowledge of them, at least in their ‘phenomenal’ con-

ception? The relation is often described as one of ‘awareness’, and it

4 P. LIVINGSTON

[6] This would make phenomenal concepts obviously different from concepts like house andcar. There is no sense in which I can gain a special kind of awareness of my car simply invirtue of having (i.e. owning) it.

[7] I defer discussion of how this works in Chalmers’ non-physicalist version of the phenome-nal concept strategy until Section III.

is, on each of the various physicalist versions of the phenomenal con-

cept strategy, this awareness that enables us to refer to them under

phenomenal concepts or modes of presentation, distinct from the

objective concepts or modes of presentation (such as neurological

concepts) that they may also stand under.

The idea of such a relation of awareness is also at the core of the tra-

ditional doctrine of acquaintance. Witness, for example, Russell’s

classic definition:

I say that I am acquainted with an object when I have a direct cognitive

relation to that object, i.e. when I am directly aware of the object itself.

When I speak of a cognitive relation here, I do not mean the sort of rela-

tion which constitutes judgment, but the sort which constitutes presen-

tation. In fact, I think the relation of subject and object which I call

acquaintance is simply the converse of the relation of object and subject

which constitutes presentation. That is, to say that S has acquaintance

with O is essentially the same thing as to say that O is present to S. (Rus-

sell, 1910, p. 108)

According to Russell, it is, moreover, at least in part by being

acquainted with certain items that we gain knowledge of them, and

can relate claims involving them to claims that do not involve objects

of acquaintance but instead embody what he calls ‘knowledge by

description’.

Since proponents of the phenomenal concept strategy generally

accept the existence of a relationship that is analogous to acquaintance

in the sense that it provides the possibility of knowing of a particular

simply in virtue of its being ‘experientially presented’ or made pres-

ent, it seems likely that their theories will be open to the problems to

which the doctrine of acquaintance has historically been prone. In par-

ticular, they will face the problem of explaining how knowledge by

acquaintance is rationally related to (judgments involving) knowl-

edge that is not, or not only, by acquaintance (for instance what Rus-

sell calls ‘knowledge by description’). At least some such judgments

(and perhaps all) have the logical form of a proposition: that is, they

attribute some general property or relation to a particular, independ-

ently characterized, object or set of particulars. But if acquaintance is

indeed a direct relation to its (particular) object, it is prima facie

unclear how an instance or item of knowledge by acquaintance can

play a role in justifying an item of propositional knowledge. For, since

acquaintance is a direct relation between a subject and an object, it

does not yet have the logical form of a proposition. Nor does the par-

ticular item with which we are acquainted. Accordingly, it is unclear

how either can play a role in justifying something with that logical

PHENOMENAL CONCEPTS & ACQUAINTANCE 5

form. Rules of deductive inference universally connect propositions

or propositional contents with other propositions or propositional

contents; there are no known rules for deduction or inference from

particulars themselves to propositionally structured judgments about

them. If the acquaintance theorist is to make sense of the role of

acquaintance in justifying knowledge of truths or the truth of proposi-

tionally structured claims, she must thus seemingly give an account of

how such justification occurs.8

It might be objected that this requirement puts too high a demand on

the phenomenal concept strategy itself. After all, one of its proponents

might object, the point of invoking phenomenal concepts is not really

(as it was, at least in part, for Russell) to give an account of the basis of

knowledge (whether by acquaintance or description), but just to exp-

lain why it may seem to be the case (even though it actually is not) that

phenomenal concepts and physical concepts must refer to ontologi-

cally distinct entities. This is, moreover, explained, at least on some

versions of the strategy, by the familiar differences between indexical

and non-indexical reference. It might therefore be thought that the

phenomenal concept strategist has no need for an account of justifica-

tion by acquaintance, that it is enough, in other words, simply to point

to these differences in referential devices in order to explain the

appearance of an explanatory gap.

To see that this is not so, consider how the phenomenal concept

strategy (in its physicalist versions) is intended to work in the first

place. It is supposed to explain the appearance of an explanatory gap

by adverting to two different ways of presenting what are in fact the

same entities: under physical concepts and under phenomenal ones.

But if the phenomenal concept theorist is to appeal to this difference in

the presentation of a specific entity, she must certainly allow that the

presentation under phenomenal concepts can yield knowledge of it, or

at least can contribute essentially to such knowledge; otherwise there

would be no relevant sense in which that presentation is a presentation

of the same entity at all. Given this, even if the phenomenal concept

strategist’s concerns are not primarily epistemological, it is reason-

able to ask for an account of this knowledge. Similarly, it is very

implausible that we can refer demonstratively (as is required by some

6 P. LIVINGSTON

[8] I do not presuppose here that proponents of acquaintance in this sense must give anaccount of a type of knowledge that, like Russell’s ‘knowledge by acquaintance’, isentirely justified by acquaintance or an acquaintance-like relationship. It could be thatacquaintance only plays a (partial) role in justifying any actual judgment, and there is nojudgment that is entirely and only based on acquaintance. Even if so, all the problems I’llraise still arise.

versions of the phenomenal concept strategy) or apply a recognitional

concept (as is required by others) to an item of which we cannot have

any knowledge through those routes. If the phenomenal concept strat-

egy is to be successful, therefore, it must allow that we have ways of

knowing about what is presented in experience on the (perhaps par-

tial) basis of this presentation, and we are owed an account of this

knowledge.9

It seems, then, that the phenomenal concept strategy must hold that

the special features of phenomenal concepts allow us to bear a relation

to our own phenomenal states that is, at least in some cases, necessary

(if not sufficient) for knowledge of their occurrence, properties, or

intrinsic character.10 But although it indeed seems plausible that we

bear some such relation to our own phenomenal states, it is far from

clear, as several recent commentators (e.g. Levine, 2007; Levin, 2007;

Chalmers, 2007) have pointed out, that physicalist adherents to the

PHENOMENAL CONCEPTS & ACQUAINTANCE 7

[9] For this specific way of putting the point, I am indebted to an anonymous referee for thisjournal. But there are other routes to the same point. For example, what the phenomenalconcept strategy is intended to explain in the first place is that there seems to be an explan-atory gap between the totality of the physical facts and facts about phenomenal conscious-ness. But the idea of such a gap is just the idea that zombies, in the sense of Chalmers(1996), are conceivable. And as Chalmers (2007) has convincingly argued, if zombies areconceivable, it is extremely plausible that whereas we are in a position to know that wehave conscious states, they are not (since they do not have conscious states). If this strat-egy is to be successful, therefore, it must explain this difference in epistemic situation: itmust explain why our beliefs formed using phenomenal concepts can count as knowledge(and hence as justified) whereas those of zombies cannot. Another way to the same point isthe following. For the physicalist versions of the phenomenal concept strategy, the differ-ence between phenomenal concepts and physical concepts turns on differences in modesof making reference to what are in fact the same things. These referential differences existalso in the case of external objects like my house or car; for instance, I can refer to myhouse demonstratively, or under an objective concept. However, there is no (even appar-ent) explanatory gap with respect to houses or cars. Thus, the explanatory gap in the caseof phenomenal states does not result simply from the semantic or referential differencebetween two modes of presentation; it must have to do with differences in justification orepistemic status as well.

[10] It might also be objected here that to hold that the appeal to phenomenal concepts mustexplain the possibility of knowledge of phenomenal states (under phenomenal concepts)is to conflate issues of justification with issues of concept formation or acquisition. But aswe have seen, the phenomenal concept strategist does owe us some account of how knowl-edge under phenomenal concepts is possible, and for all versions of the phenomenal con-cept story, the story about how phenomenal concepts are formed or acquired will play anintegral role in this account. For it is, after all, the special features of phenomenal conceptsthat are being appealed to in order to explain how phenomenal knowledge differs from thesort of knowledge we might have of (what are said to be) the same states under physicalconcepts. The phenomenal concept strategist will, moreover, face this burden regardlessof the nature of her specific account of justification; even if, for instance, she adopts a pro-cess reliabilist account of the justification of beliefs involving phenomenal concepts, shewill still owe us an account of how the relevant process functions to yield the requisite kindof knowledge (i.e. under phenomenal rather than physical concepts). I would like to thankAlvin Goldman for some discussion of these issues.

phenomenal concept strategy can actually make sense of this kind of

relationship at all. The problem is that the thoroughgoing physicalist,

in giving a theory of phenomenal concepts, can only seemingly appeal

to or make use of qualities and relationships that can ultimately be

accounted for in physical terms: qualities like shape, size, and mass,

and relationships like physical constitution, containment, and causa-

tion. But it is unclear how any of these properties and relations, or any

combination thereof, could account for the special experiential rela-

tion (of presentation or its converse, acquaintance) that the phenome-

nal concept strategy requires. Given physical states possessing any

combination of physical properties and relations, it is still evidently

mysterious why that combination of properties and relations should

add up to anything like awareness of the relevant states. And simply

talking of the way that the presence or ‘presentation’ of the relevant

states is related to the formation of their phenomenal concepts does

not seem to help. For if this is not just a metaphor, then the ‘presence’

at issue must, for the physicalist, simply be physical presence, the

actual occurrence of an (instance of a) neurological state within the

brain. But as Levine (2007, p. 163) has pointed out, physical presence

does not amount to cognitive presence. No matter how much reason I

have to believe that a particular state is occurring inside of my brain,

this does not by itself seem to give any reason to believe that I am

aware of that state in the experiential, first-person sense.

More generally, the phenomenal concept strategy has to account for

how we get to be in a special experiential relation to our phenomenal

states, one that amounts to awareness of them under phenomenal (as

distinct from physical) concepts. But to the extent that these theories

actually explain this relation, they do so by appealing to what we

might call content properties of these states or their tokens, properties

such as that of having a certain phenomenal content or phenomenal

‘character’ or falling under a certain phenomenal type.11 But on all

versions of the phenomenal concept strategy, phenomenal concepts

themselves inherit their content — their ability to group like individu-

als and distinguish them from unlike ones — only from the presence

of, or direct indexical reference to, particular token individuals. The

idea, on each version of this strategy, is that direct reference to a par-

ticular phenomenal state, or the actual inclusion of such a particular in

the concept, is what gives the concept the content that it has. Clearly,

though, if the phenomenal content is to ‘take up’ the content of a

8 P. LIVINGSTON

[11] This kind of ‘character’ is, of course, to be distinguished from the ‘character’ ofindexicals, as in Kaplan (1989).

particular occurrent phenomenal state in this way, the phenomenal

state must already have the content that is to be taken up. But now the

problem becomes clear: token individuals don’t even have content

except as tokens of the types they are tokens of. It makes no sense to

treat a particular token of a red experience, for instance, as a red expe-

rience, unless we already know that we are entitled to treat it as being

of the same type as other red experiences.

With respect to justification, therefore, the phenomenal concept

strategy thus seems to face a dilemma. First, we may assume that the

phenomenal particular tokens already have, as tokens, determinate

content properties, for instance the property of being a token of a par-

ticular phenomenal quality type. If we do this, we may be able to

explain how these content properties are inherited by subsequent con-

ceptual judgments (at any rate, it seems we will have taken a necessary

step toward this explanation). But to do this is already to assume that

(some of) our conceptual judgments about these particulars (judg-

ments, for instance, about what types they are tokens of) are justified,

and hence it is to fail to give an explanation for this justification.

Alternatively, we may refuse to treat them this way: we may take phe-

nomenal particulars not to have content properties until they are

brought under concepts, for instance in a basic phenomenal judgment.

But then it will be impossible to appeal to the content properties of the

token states themselves in explaining how the content of these judg-

ments is indeed ‘inherited’ or ‘taken up’ (as the phenomenal concept

strategy demands) from them. How does the mere presence of an item

help to yield a concept of its type, or to justify a judgment about it? It

seems clear that it does so only in that I am able to recognize it or its

properties, to bring it under a concept or concepts. But if we are going

to account for such justification, we must not beg the question of its

content at the outset.

The phenomenal concept strategy, whether deployed by physical-

ists or anti-physicalists, thus appears to require a distinctive and prob-

lematic relation of aquaintance. Interestingly, in fact, recognition of

the way that they are committed to some form of the doctrine of

acquaintance has the effect of grouping proponents of the phenomenal

concept strategy together (whether they are physicalists or anti-phys-

icalists about the ‘nature’ of the relevant states), and opposing them to

those (mostly physicalists) who deny the possibility of knowledge by

acquaintance. The question whether there is, in fact, such a way of

knowing, is plausibly a very deep issue underlying the debate about

the role of consciousness in the objectively describable (physical)

world. For if we do not believe in acquaintance, there is little reason to

PHENOMENAL CONCEPTS & ACQUAINTANCE 9

think that consciousness poses any special problem for physicalistic

explanation; and if we do believe in it, it may be relatively insignifi-

cant whether the particulars with which we can be acquainted in fact

turn out to be ontologically ‘physical’ or ‘non-physical’.12

II

Beginning in the 1920s, discussion in the Vienna Circle took up the

question of the relationship of first-person, direct empirical knowl-

edge to the objective claims and theories of science. The result of this

discussion was the debate over the form of ‘protocol sentences’ that

ultimately divided Moritz Schlick from his Circle colleagues Rudolf

Carnap and Otto Neurath and remained substantially unresolved when

the Circle finally broke up in the 1930s. The crux of this debate was

the right way to describe the form of sentences directly reporting the

ultimate justificatory basis in first-person experience of the (objective

and third-person) empirical claims of science. According to Schlick,

protocol sentences, as reports of first-person experience, must always

also have a first-person form. For instance, a typical protocol sentence

might be ‘I am experiencing red here now’. The sentence makes

ineliminable use of indexicals, and does not preserve its meaning

when uttered by another individual or at another time and place.

Neurath, by contrast, held that protocol sentences, as the ultimate jus-

tificatory basis for third-person scientific claims, should always from

the outset have a third-person, objective form. For instance, a protocol

reporting a basic observation might be ‘Otto observes that the pointer

is at (x,y,z,t)’, where the sentence is completed with a specification of

(objective) spatio-temporal coordinates. The sentence makes no use

of indexical terms and makes reference to individuals only under

third-person, objective terms such as might be used with the same

meaning by anyone, on any occasion.

Although they disagreed about the form of the protocol sentences,

both Schlick and Neurath shared with most of the rest of the Vienna

Circle an understanding of the logical form of objectivity and objec-

tive scientific knowledge itself. According to the conception that they

10 P. LIVINGSTON

[12] In the preceding, I have assumed that acquaintance is always a relation to particulars. Ofcourse, some proponents of acquaintance, including Russell, have held that in addition toacquaintance with particulars, there is also acquaintance with universals or types. If wemay indeed appeal to acquaintance with universals, then we may perhaps account for theapplication of phenomenal concepts as grounded in demonstratives or indexicals referringto those universals. However, the question of how we succeed in making such reference touniversals, or actually using it to ground further judgments, remains unresolved. (It doesnot seem sufficient simply to assume that we can demonstratively refer to general typessimply by referring to one or more particulars that instantiate them.)

shared, all objective claims can be put in the form of what Carnap

called structural definite descriptions or structure statements. These

statements include no indexical or first-personal terms and make no

mention of any individual’s own experiences. Moreover, their refer-

ring terms, including terms for basic objects, are defined purely

relationally; on the structuralist conception, it is always possible to

define these terms without the need to indicate or demonstrate any

particular object. It was Carnap’s hope, in particular, that all of the

sentences of science could be put in the form of such descriptions, and

in The Logical Structure of the World he outlined an ambitious prog-

ramme for ‘structuralizing’ the claims of the various branches of sci-

ence to bring them within the logically unified corpus of science

(Carnap, 1928/1967, Section 16). Because structuralization allows

scientific claims to be put in the form of claims about physical (spatial

and temporal) locations and positions, this structuralist conception of

knowledge and objectivity formed the basis for what Neurath initially

termed physicalism, the doctrine that all objective claims can be trans-

lated into a single, logically unified language, which Neurath called

the ‘physical language’. This linguistic doctrine is the direct historical

and conceptual ancestor of contemporary ‘physicalism’, although the

contemporary doctrine is more often understood as an ontological or

metaphysical, rather than a linguistic or semantic, one (Livingston,

2004, Chapters 2 and 5).

If physicalism, in Carnap and Neurath’s sense, is true, then it ought

to be possible to describe the totality of (objective) facts in structur-

alized propositions; by defining the ultimate logical structure of these

propositions, it would be possible to define the logical structure of the

world itself. But the structuralist conception of meaning and objectiv-

ity encountered, almost immediately, a deep and problematic founda-

tional question. This is the question of the relationship between

logical structures of relation and what they are structures of: the basic

elements or entities whose relations of similarity and difference were

to define the entirety of the logical structure of the world. It was the

problem of these relations — and in particular, how the intrinsic

nature of elements could play a role in justifying the structural claims

expressed their relations of similarity or difference — that led directly

to the protocol sentence debate.

In 1932, Moritz Schlick delivered three lectures under the collec-

tive title ‘Form and Content: An Introduction to Philosophical Think-

ing’ (Schlick, 1932/1979). In the lectures, he sought to describe the

condition for any possibility of communicating thought linguistically.

Such communication, he held, always amounts to the communication

PHENOMENAL CONCEPTS & ACQUAINTANCE 11

of structure. In each case, however, in order for understanding actu-

ally to occur, it would be necessary for the ‘structure’ or ‘form’ of lin-

guistic signs to be ‘filled in’ with ‘content’ drawn from individual

experience (ibid., p. 296). With respect to verification, Schlick held

that it was the possibility of such direct ‘filling in’ that allows empiri-

cal propositions ultimately to be justified by experience. In actually

verifying an empirical proposition, Schlick thought, we must in each

case perform a subjective act of ‘comparing’ the proposition to reality

by ‘filling in’ the content of the proposition from experience itself.

This claim about verification led him to propose his theory of ‘affir-

mations’ or Konstatierungen as lying ultimately at the epistemic basis

of empirical knowledge.

According to this theory, affirmations essentially contain demon-

strative or indexical terms directing that a certain kind of ‘gesture’ or

‘pointing’ to reality actually occur. For instance, an affirmation such

as ‘Here now blue is bounded by yellow’ necessarily contains demon-

strative terms such as ‘here’ and ‘now’; and the ‘rules of use’ for such

terms as they are used in an affirmation ‘stipulate that in making the

statement in which they occur, an experience occurs’ and ‘attention is

directed to something observed’ (Schlick, 1934/1959). Schlick’s the-

ory of affirmations thus amounts to a theory of acquaintance.13 More-

over, like many contemporary versions of the phenomenal concept

strategy, it expresses this theory as the requirement that ultimate

justifiers have an indexical form.

The price of this solution, however, is the essential incommunica-

bility of affirmations. For given that linguistic communication is

always the transmission of structures, and the content attached to them

can never be intersubjectively verified or assured, it is a direct conse-

quence of Schlick’s view that affirmations are strictly incommunica-

ble and therefore cannot be expressed or communicated by any terms

or sentences of public language. This price was too steep for some.

Neurath, in particular, attacked Schlick’s conception of the basis of

empirical knowledge in a series of articles beginning in 1931

(Neurath, 1931/1983; 1932/1959; 1934/1983). Though Neurath put

his objection in terms of his ‘physicalist’ view that all language must

be structural language, beyond this linguistic thesis there is also a sub-

stantial epistemological problem that Neurath finds with Schlick’s

account of verification in terms of ephemeral and inexpressible ‘affir-

mations’. The problem is this: if affirmations are indeed to serve as a

12 P. LIVINGSTON

[13] It does not, however, amount to a theory of knowledge by acquaintance — Schlickexplains clearly that acquaintance, although it is the foundation of knowledge, does not,for him, amount to knowledge by itself.

justificatory basis for knowledge, they must be able to play a role in

justifying structural propositions. Now, in so far as these propositions

are meaningful, they have meaning by describing the structural rela-

tions their objects bear to one another. But if this is right, then it seems

evident that the justification of any structural proposition is entirely a

matter of the relations it ascribes among its objects. Thus, the justifi-

cation of any structural proposition ought to be expressible entirely in

terms of other structural propositions. But this is just what Schlick’s

theory of affirmations denies. In so far as it holds that certain struc-

tural propositions, for instance public propositions describing my

own states of mind, are justified in part by affirmations that are not

structural, Schlick’s theory holds that the justification of some struc-

tural propositions is not a matter of structure at all, but instead

depends on the role of non-structural ‘content’ in filling them in.

These propositions, on Schlick’s view, are justified, at least in part, in

a way that has nothing to do with their relation to other structural

propositions. But how they can be so justified, then, seemingly

remains mysterious and unexplained.

We might call this the problem of ‘non-structural justifiers’; it

underlies many of the problems about justification, acquaintance, and

the possibility of ‘private language’ that subsequent philosophers

have raised against empiricist theories.14 The problem of non-struc-

tural justifiers arises because it is plausible that structural proposi-

tions, if they are justified at all, are justified entirely by other

structural propositions. Might we agree to this, holding that all justifi-

cation of structural propositions is indeed structural, but that some

structural propositions, for instance propositions about the similarity

or difference of phenomenal experiences, are neither justified nor

unjustified, but can nevertheless be known and thereby can serve as

the (partial) justificatory basis for further structural propositions (we

might call such propositions ‘basic’ structural ones)?15 This yields an

account on which there are indeed no non-structural justifiers but

which nevertheless might preserve much of Schlick’s picture of

non-structural contents as ‘filling in’ certain structural claims. The

problem, however, is just that it is now difficult to see how we can

account for the correctness of these ‘basic’propositions about similar-

ity and difference, if they are not themselves justified by other struc-

tural propositions. It is plausible that the correctness of judgments of

PHENOMENAL CONCEPTS & ACQUAINTANCE 13

[14] Examples might be thought to include Sellars’ (1955) attack on the ‘Myth of the Given’and Wittgenstein’s (1953/2001) celebrated ‘private language argument’.

[15] This line of response was suggested to me by David Chalmers in correspondence.

similarity and difference is conceptually linked to the possibility of

acts of comparison. If it is meaningful to say that two items are similar

to or different from one another in a particular respect, it must be at

least possible for them to be compared with one another in that

respect; the proposition saying that they are similar or different will be

correct if, and only if, such an (actual or possible) act would reveal

them to be so.16 Thus, if ‘basic’ structural propositions are to be con-

strued as correct and knowable (as it seems they must be if they are to

be available to serve for further justification), it appears they must be

construed as justified by other structural propositions after all. It thus

appears incoherent to suppose there could be ‘basic’ structural

justifiers that are not themselves justified or unjustified, but are

nevertheless available for use in further justification.

Alternatively, it might be thought that a structural proposition about

the similarity or difference of two particulars could be justified by

non-structural propositions in the following way: I might judge of a

particular that it is red and simultaneously judge of another that it is

orange, and on this basis reach the (justified) structural judgment that

the two particulars are different in colour.17 The first two judgments

might be thought to be non-structural, in that they do not obviously

directly involve or ascribe relations between particulars, but they

might jointly be thought to justify the third, structural, judgment.

There are two problems with this, however. First, it is not clear that the

monadic judgments of colour are indeed non-structural in the relevant

sense. For philosophers such as Schlick and Carnap, at any rate, judg-

ments of even directly perceptible properties such as the colour of par-

ticulars are structural, since their possibility is dependent upon the

complex total structural network of similarities and differences that

defines the relations of colours to one another and the position of

objects in the visual field and in space. But second, even if we can

consider the first two judgments in themselves and independently of

these constitutive structural patterns of similarities and differences,

we must take care in specifying their actual content. If the two judg-

ments are specifiable as judgments about recognizably distinct and

nameable objects, e.g. ‘the triangle is red’ and ‘the square is orange’,

then they are clearly already structural judgments in the relevant

14 P. LIVINGSTON

[16] This is not to say that such an act of comparison must actually be carried out by the subjectin order for the judgment of similarity or difference to be correct (or justified). It is just tosay that the correctness of such a judgment of similarity or difference is conceptuallydependent upon the possibility of such an act.

[17] This paragraph responds to an objection formulated by an anonymous referee for thisjournal.

sense. If, on the other hand, we suppose (in accordance with Schlick’s

theory) that the objects are picked out solely by private and incommu-

nicable demonstratives or demonstrative-like devices, e.g. ‘this1 is

red’ and ‘this2 is orange’ (or perhaps ‘red here1 now’ and ‘orange here2

now’), then we must, at least, suppose that there are two distinct

(token) demonstrative devices available and that the two devices

indeed pick out distinct particulars. For otherwise there will be no way

to use the two judgments in the justification of the subsequent judg-

ment of difference. But the justification of this supposition is depend-

ent upon, at minimum, that of a judgment that the objects of the two

demonstrative devices are indeed (numerically) distinct. Either way, it

is possible to hold that non-structural propositions (if any such there

be) play a role in justifying structural ones, individually or jointly,

only if there are also other structural propositions available to play a

supplemental role; thus it appears, again, impossible for a structural

proposition to be justified wholly by non-structural ones.

III

As noted, the phenomenal concept strategy comes in (ontologically)

physicalist and non-physicalist versions, but as I have argued, phe-

nomenal concept theorists of both types are committed to some ver-

sion of justification by presence. The best and clearest contemporary

account of such justification is given by Chalmers (2003; 2007), who

is a non-physicalist proponent of the strategy. I turn to consideration

of his account of the justification of phenomenal beliefs, with a view

to locating the explanatory problems that still remain unsolved.

On Chalmers’ view, a phenomenal belief, such as my belief that (as

I might put it in public language) I am having an experience of red-

ness, can be justified (in part, at least) by the occurrence of an experi-

ence with the relevant quality (in this case, phenomenal redness). Ref-

erence to such a quality is accomplished, first, through an act of

demonstration, typically the fixation of one’s attention upon the par-

ticular experience (and its phenomenal quality) one is having.18 This

suffices to yield what Chalmers calls a ‘demonstrative’ phenomenal

concept E, which functions together with the act of demonstration to

pick out whatever quality the subject is currently (inwardly) demon-

strating. Here, the analogy is to the linguistic functioning of indexical

and demonstrative terms like ‘I’ and ‘that’; the demonstrative concept

PHENOMENAL CONCEPTS & ACQUAINTANCE 15

[18] There are questions to be asked about the intelligibility of such an act of ‘inward demon-stration’, but I do not pursue them here.

functions only together with a demonstration to pick out the quality

that is being demonstrated.

According to Chalmers, however, this demonstrative concept is dis-

tinct from what he terms a pure phenomenal concept of the same qual-

ity. Such a concept picks out the phenomenal character of an

experience directly and non-relationally, ‘in terms of its intrinsic phe-

nomenal nature’ (Chalmers, 2003, p. 4). We can understand the differ-

ence between indexical and pure phenomenal concepts by considering

what Mary (in the famous thought experiment due to Jackson, 1982)

learns when she leaves the black-and-white room and learns for the

first time what it is like to see red. On Chalmers’ view, having formed

the demonstrative concept E which allows her to refer to the quality

she is now experiencing, she can now form the pure phenomenal con-

cept R, and now learns the identity E = R. This new belief is analogous

to other cases of beliefs identifying the objects of demonstratives

under non-demonstrative concepts, for instance the beliefs (that I

might put as) I am N.N., that object is tall, or the time is now 4:48.

These concepts are, as Chalmers suggests, plausibly distinct from

any publically expressible concept of phenomenal qualities. Such

concepts (for instance the concept ‘what members of the community

normally refer to as red’) have their reference fixed relationally, for

instance by reference to behaviour or external stimuli, whereas pure

phenomenal concepts are to make direct reference to the phenomenal

properties of their objects (Chalmers, 2003, p. 15). In the most typical

case, the content of a pure phenomenal concept, and hence the justifi-

cation of a belief I form with it, is directly determined by the quality of

an experience I am currently having. Chalmers calls such pure phe-

nomenal concepts ‘direct’ phenomenal concepts and suggests that in

these cases we may, in fact, think of a ‘direct’ phenomenal concept as

partially constituted by the very quality it refers to (ibid., p. 12). Thus,

for Chalmers it is possible for (token) instances of phenomenal prop-

erties themselves to partially constitute (perhaps along with other

constituents) direct phenomenal concepts predicated of them. More-

over, it is possible to use these concepts to form direct phenomenal

beliefs about the experiences in question.

When a direct phenomenal concept is formed, it is plausible, as

Chalmers notes, that it will be ephemeral. Since it must include the

very quality-instance to which it refers, it seems it will remain in exis-

tence only as long as that quality-instance does (i.e. only as long as the

subject is experiencing the quality in question). However, according

to Chalmers, it is also possible to form another kind of pure phenome-

nal concepts that are not direct, what he terms ‘standing’ phenomenal

16 P. LIVINGSTON

concepts. Such phenomenal concepts, like direct ones, pick out the

phenomenal qualities of experience directly. Nevertheless, they may

exist and are available for use in forming beliefs even after the

qualities to which they refer disappear.

Now, it is far from obvious how we should think of the partial con-

stitution of concepts by property-instances, in Chalmers’ sense. Since

the sense of ‘constitution’ here is explicitly not physical or material,

we seemingly must rely on the metaphor of the ‘taking up’ of prop-

erty-instances within concepts to understand constitution, in the rele-

vant sense. However, as Chalmers argues, it is plausible that in

addition to this ‘natural’ relationship of partial constitution, there is a

distinctively epistemic relationship (perhaps underlain by partial con-

stitution) between phenomenal property-instances and the direct phe-

nomenal concepts which characterize them. Chalmers in fact calls this

relationship ‘acquaintance’. On Chalmers’ view, acquaintance is a

relation that we bear only to phenomenal properties instantiated in our

experience, and ‘most directly’or primarily to instances of these prop-

erties (ibid., pp. 21–2). And it is only in virtue of our bearing this rela-

tion to property-instances that we are able to form direct phenomenal

concepts of them at all. The defining characteristic of acquaintance is

that, as Chalmers puts it, ‘whenever a subject has a phenomenal prop-

erty, the subject is acquainted with that phenomenal property’ (ibid.,

p. 22; cf. Russell’s definition, above).

Like all versions of the phenomenal concept story, Chalmers’

account thus rests centrally on the possibility of justification in virtue

of acquaintance. In particular, if Chalmers’ view is to be successful,

then it must be possible for my acquaintance with a phenomenal prop-

erty-instance on a particular occasion to play a necessary role in justi-

fying (perhaps along with other auxiliary and standing concepts) my

judgment that, for instance (as I can express it in public-language

terms) I am having a red experience right now or even I was having a

red experience two hours ago.19 In terms of Chalmers’ framework for

distinguishing among types of phenomenal concepts, there are really

two distinct questions here. The first question is: how does my merely

having or experiencing a phenomenal property instance (and thus

being acquainted with it) confer justification (or help to confer

PHENOMENAL CONCEPTS & ACQUAINTANCE 17

[19] Additionally, it seems that these judgments must be expressible in public-language termseven though these terms must also refer to phenomenal properties. For if, as Chalmerssometimes suggests, the term I use to refer to a phenomenal quality is distinct from anypublic-language term, it is again obscure how justification of a proposition using phenom-enal-quality terms can carry over into the justification of such public-languageexpressions.

justification) upon the judgment I make about it using a direct phe-

nomenal concept? But another, related question is: how does a judg-

ment formed using a direct (and hence, ephemeral) phenomenal

concept confer justification (or help to confer justification) upon a

judgment made using a standing phenomenal concept?

With respect to the first question, the underlying problem is again

that phenomenal experiences are particular, datable occurrences; and

so any acquaintance or acquaintance-like relation to one of them is a

relation to a particular. Although Chalmers suggests that he thinks of

acquaintance as, at least potentially, acquaintance with a property, he

realizes that it must be, first and foremost, a relationship to an instance

of a property.20 The problem, then, is that it remains unclear how any

sort of relationship to a token individual can justify (or even help to

justify) a judgment involving concepts, which must be justified (if it is

justified at all) as a type. For this, as we have seen, it is not sufficient

simply to appeal to the possibility of demonstrative direct reference to

the particular in question. For however successful this kind of refer-

ence might be, it cannot by itself ground either more general knowl-

edge of the type of which the particular individual is an instance, or (a

fortiori) subsequent judgments about what belongs to this type.

In introducing pure (direct) phenomenal concepts, Chalmers draws

an analogy between the types of judgments we may make using them

and other beliefs ‘in which the object of a demonstrative is independ-

ently characterized’. Since it is, on Chalmers’ account, only by an act

of (or akin to) demonstration that we first secure reference to a phe-

nomenal experience at all, it seems evident that the most basic judg-

ments using a pure phenomenal concept must take the form of an

identification of the object of such a concept with the object of a dem-

onstrative term, for instance E = R (where E is a demonstrative and R

is a pure phenomenal concept). He says that such identities are just ‘as

cognitively significant’ as other judgments that identify or attribute a

property to something picked out by a demonstrative, for instance the

judgment (that I might express by saying) that object is tall or (we

may suppose) now is 3:15.

But actually it is far from obvious that the identity E = R can take

this kind of (cognitively significant) form. For in these cases of

18 P. LIVINGSTON

[20] ‘Acquaintance can be regarded as a basic sort of epistemic relation between a subject and aproperty. Most fundamentally, it might be seen as a relation between a subject and aninstance of a property. I am most directly acquainted with this instance of phenomenalgreenness. This acquaintance with an instance can then be seen to confer a derivative rela-tion to the property itself’ (Chalmers, 2003, p. 22). Needless to say, whether acquaintancewith an instance indeed does suffice to give us a relation to ‘the property itself’ is just whatis at issue here.

informative predication of an object picked out by demonstrative ref-

erence, it is presupposed that there are independently available non-

demonstrative concepts (for instance tallness) that can be used to

predicate of those objects the properties thereby ascribed to them. The

ascription itself presupposes the ability to use these concepts inde-

pendently, to predicate them of other objects, etc. But in the phenome-

nal concept case, where the concept is supposed to be formed de novo,

it is far from obvious that we have this ability, or how we are to gain it

if we do not have it. This is, again, just the same problem I have

repeatedly discussed: concept possession plausibly involves the abil-

ity to identify and re-identify particulars of the same type; but refer-

ence to an individual by itself does nothing to account for this ability.

If, however, we cannot assume that demonstrative reference to an

individual suffices to yield the ability to form a non-demonstrative

‘type concept’ whose possession itself implies the ability to identify

and re-identify members of the type, then there is no reason to suppose

the identities we are in a position to assert after forming such a concept

are indeed cognitively significant at all. Rather than allowing us to

independently characterize the object of a demonstrative, they would

then seem capable, at best, only of allowing us to characterize the

object demonstratively twice over. Rather than having the form, for

instance, ‘now is 3:15’ or ‘that object is tall’, they would have a form

such as ‘now is the current time’ or ‘that object [demonstrating a par-

ticular object] is as tall as that object [demonstrating the same object

again]’ (cf. Wittgenstein, 1953/2001, para. 279). But if this is their

form, it is clear that they can play no substantial role in the justifica-

tion of further, non-demonstrative judgments involving phenomenal

(or any other type of) concepts.

As Chalmers in fact suggests, the general problem arises again with

respect to what he terms standing phenomenal concepts. Since direct

phenomenal concepts are ephemeral, it is unclear how the justification

of their application (which, on Chalmers’ account, involves the pres-

ence of phenomenal particulars and survives only as long as they are

present) can carry over to the justification of the application of stand-

ing phenomenal concepts descending from them, which are not ephe-

meral in this way. As Chalmers says, in order to account for this, we

need an account of how a judgment using standing phenomenal con-

cepts can ‘inherit’ its justification from a judgment involving only

direct phenomenal concepts. Though he admits that he does not have a

general account of the inheritance of justification by tokens (or ‘phys-

ical vehicles’) of phenomenal concepts (indeed, as he says, nobody

does), Chalmers suggests that we might be able to solve the problem

PHENOMENAL CONCEPTS & ACQUAINTANCE 19

simply by combining sameness of content with an appropriate causal

relationship. More generally, he says, we need ‘a “typing” of concepts

and beliefs that is more fine-grained than a mere typing by content,

but less fine-grained than a typing by numerical identity of tokens’

(Chalmers, 2003, pp. 29–30).

However, if what is needed is not simply to describe but rather to

explain the inheritance of content, it is clear that this will not do. For if

sameness of content between two phenomenal concept-tokens, A and

B, is supposed to be (so much as) necessary in order for B to ‘inherit’

justificatory properties from A (i.e. for a judgment involving B to

inherit justificatory properties from a judgment involving A), then in

order to make sense of the ‘inheritance’ relation we need an under-

standing of how A and B can share the same content. But when A is a

token of a direct phenomenal concept, and B is a token of a standing

phenomenal concept, it is not at all clear that we have this understand-

ing. For the content of A is (or at least is largely constituted by) a par-

ticular phenomenal experience; whereas the content of B is not. In

particular, it is unclear how the content of a direct phenomenal con-

cept (which is, after all, ephemeral and can only be applied for a lim-

ited time, and hence to a limited range of objects (perhaps only one))

can be ‘the same’ as that of a standing phenomenal concept (which is

enduring and can be applied to a potentially unlimited number of

objects, or at least to the same object whenever it occurs). Similarly, it

is puzzling how a judgment that does not employ a standing phenome-

nal concept (but only a direct one) can help to support a judgment that

does employ a standing phenomenal concept, since it is clear there

cannot be a deductive relationship between a judgment of the first

type and a judgment of the second, and it is not obvious what other

form such a justificatory relationship could take.21

IV

In this paper, I have not attempted to solve the problem of acquain-

tance, but have simply tried to show how it arises for both physicalist

and non-physicalist proponents of the phenomenal concept strategy

alike. This appears to be a deep problem, one which will probably

remain with us for some time. For as I have repeatedly emphasized, it

is extremely prima facie plausible that there is an acquaintance-like

relation that we can bear to our own experiences in virtue of which we

can have knowledge of (i.e. justified true beliefs about) their intrinsic

20 P. LIVINGSTON

[21] I am indebted to an anonymous referee for this journal for the formulation of the precisepoint in this sentence.

character. But it seems there is, so far at least, no good answer to the

question of how such a relation can indeed play a role in justification.

Although it is very plausible that there are non-structural justifiers,

the prospects for integrating them into an otherwise structuralist

account of justification in a way that is both plausible and genuinely

explanatory thus seem to be quite dim. But it seems we must give, at

least in large part, a structuralist account of justification, since at least

most justification, and the only kind of justification we now under-

stand, is structural. The issue of what it would take to give an account

that satisfies all of the natural explanatory demands here runs deep.

Since the underlying issue is not really one of different types of fla-

vours or justification at all, but indeed of what justification is, it is not

clear that we can solve it without considering more deeply such mat-

ters as the nature of generality, the relationship of individuals to what-

ever types they ‘fall under’, and what is involved in the predication of

concepts of individuals itself. At the same time, the problem is closely

connected to the problem of how it is possible for there to be a distinc-

tion between the ‘objective’ and the ‘subjective’ at all: how, in other

words, certain organisms come to be able to have a perspective or a

first-person point of view, how they come to be able to use indexical

terms to refer to themselves and to their current location in space and

time.22

References

Carnap, R. (1928/1967) The Logical Structure of the World, George, R.A. (trans.),Berkeley, CA: University of California Press.

Chalmers, D.J. (1996) The Conscious Mind: In Search of a Fundamental Theory,New York: Oxford University Press.

Chalmers, D.J. (2003) The content and epistemology of phenomenal belief, inSmith, Q. & Jokie, A. (eds.) Consciousness: New Philosophical Perspectives,Oxford: Oxford University Press. (Page # references are to the online version:http://consc.net/papers/belief.html)

Chalmers, D.J. (2007) Phenomenal concepts and the explanatory gap, in Alter, T.& Walter, S. (eds.) Phenomenal Concepts and Phenomenal Knowledge,Oxford: Oxford University Press.

Ismael, J. (1999) Science and the phenomenal, Philosophy of Science, 66, pp.351–369.

Jackson, F. (1982) Epiphenomenal qualia, Philosophical Quarterly, 32, pp.127–136.

Kaplan, D. (1989) ‘Demonstratives’ and ‘Afterthoughts’, in Almog, J., et al. (eds.)Themes From Kaplan, Oxford: Oxford University Press.

PHENOMENAL CONCEPTS & ACQUAINTANCE 21

[22] I would like to thank David Chalmers and Kelly Becker for helpful discussion of earlierdrafts of this paper. I would also like to thank the audience at an ANU philosophy researchcolloquium in June 2011, where an earlier version was presented.

Levin, J. (2007) What is a phenomenal concept?, in Alter, T. & Walter, S. (eds.)Phenomenal Concepts and Phenomenal Knowledge, Oxford: Oxford Univer-sity Press.

Levine, J. (2007) Phenomenal concepts and the materialist constraint, in Alter, T.& Walter, S. (eds.) Phenomenal Concepts and Phenomenal Knowledge,Oxford: Oxford University Press.

Livingston, P.M. (2004) Philosophical History and the Problem of Consciousness,Cambridge: Cambridge University Press.

Loar, B. (1997) Phenomenal states, in Block, N., Flanagan, O. & Güzeldere, G.(eds.) The Nature of Consciousness, Cambridge, MA: MIT Press.

Loar, B. (1999) Should the explanatory gap perplex us?, in Rockmore, T. (ed.)Proceedings of the Twentieth World Congress of Philosophy, vol. 2, BowlingGreen, OH: Philosophy Documentation Center.

Neurath, O. (1931/1983) Physicalism, in Neurath, O., Philosophical Papers,1913–1946, Vienna Circle Collection, vol. 16, pp. 52–57, Cohen, R.S. &Neurath, M. (ed. and trans.), Dordrecht: Reidel.

Neurath, O. (1932/1959), Protocol sentences, in Ayer, A.J. (ed.) Logical Positiv-ism, pp. 199–208, New York: The Free Press.

Neurath, O. (1934/1983), Radical physicalism and the ‘real world’, in Neurath, O.,Philosophical Papers, 1913–1946, Vienna Circle Collection, vol. 16, Cohen,R.S. & Neurath, M. (ed. and trans.), Dordrecht: Reidel.

Neurath, O. (1983), Philosophical Papers, 1913–1946, Vienna Circle Collection,vol. 16, Cohen, R.S. & Neurath, M. (ed. and trans.), Dordrecht: Reidel.

O’Dea, J. (2002) The indexical nature of sensory concepts, Philosophical Papers,31, pp. 169–181.

Papineau, D. (2002) Thinking About Consciousness, Oxford: Clarendon Press.Perry, J. (1979) The problem of the essential indexical, Nous, 13, pp. 3–21.Perry, J. (2001) Knowledge, Possibility, and Consciousness, Cambridge, MA:

MIT Press.Russell, B. (1910) Knowledge by acquaintance and knowledge by description,

Proceedings of the Aristotelian Society, 11, pp. 108–128.Schlick, M. (1932/1979) Form and content, in Mulder, H.L. & Van de Velde-

Schlick, B.F.B. (eds.) Philosophical Papers, vol. 2, Dordrecht: Riedel.Schlick, M. (1934/1959) The foundation of knowledge, in Ayer, A.J. (ed.) Logical

Positivism, New York: The Free Press.Sellars, W. (1955) Empiricism and the philosophy of mind, Minnesota Studies in

the Philosophy of Science, 1, pp. 253–329.Wittgenstein, L. (1953/2001) Philosophical Investigations, 3rd ed., Anscombe,

G.E.M. (trans. with revisions), Rhees, R., Anscombe, G.E.M. & von Wright,G.H. (eds.), Cambridge, MA: MIT Press.

Paper received April 2012; revised September 2012.

22 P. LIVINGSTON